This invention relates to an ink mist type high speed printer.
The increasing trend toward speed-up of the central processing unit of the electronic computer system is necessitating corresponding speed-up of the printers which are out put terminal units of such computer system. There are known various types of high speed printers among which is a so-called ink mist type high speed printer in which the ink mist particles electrically charged by the ions are moved to the recording paper by an electrostatic force to thereby print the desired characters, etc., by way of dot matrices.
FIG. 1 shows diagrammatically the printing section of a known ink mist type high speed printer. According to this printer, a positive electrode (second electrode) 2 called as corona wire and a negative electrode (first electrode) 4 surrounded by an insulator 3 are arranged in opposition to each other so that a recording paper 1 fed at high speed passes therebetween, and a high voltage of several thousand volts is applied between these two electrodes. The first electrode 4 is housed in a back bar 5 adapted to hold the recording paper 1 at the correct printing position. Provided between said back bar 5 and second electrode 2 is an aperture board 6 designed to serve as a gate means for controlling movement of the ions. In the upper portion of said aperture board 6 are provided a plurality of apertures 7 arranged along the length of the aperture board (6) for allowing passage of the ions. Between said aperture board 6 and recording paper 1 is formed a stream of ink mist 10 as the ink particles are supplied in an atomized form from a mist tank 8 along with air from an air outlet 9. The cations impinge against this stream of ink mist to let the ink particles migrate toward the first electrode 4. Thus, if the cations are selectively passed by controlling the direction of the electric field in said apertures 7, the ink particles are deposited in the form of a matrix pattern on the recording paper 1.
In such known high speed printer, the first electrode 4 is constituted from a single piece of conductor common to the entire printing area. Therefore, when printing is made on a paper which is smaller in width than the ordinary (standard) printing paper, a certain portion of the back bar 5 is directly positioned in the space where the ions move, that is, such portion is opposed to the aperture board 6 with no interposition therebetween. In such a case, flocks from the recording paper 1 or dust in the air could deposit on the back bar 5, and such dust is charged negatively and attracted to the aperture board 6 which is higher in potential than the first electrode 4. As such dust passes through the ink mist, it is impregnated with ink particles to cause soiling of the aperture board 6 or clogging of the apertures 7. If such situation is produced, the cations become unable to pass the apertures 7, and the common electrode 11 provided on the front side of the aperture board 6 and the selection electrode 12 provided on the back side thereof become conductive to each other to disenable control of passage of the cations. This gives rise to various problems such that no printing is made on the paper portion corresponding to such trouble area when printing is performed thereafter on a normal-sized printing paper, or that the printing quality is reduced.